Photovoltaic cells, sometimes called solar cells, can convert light, such as sunlight, into electrical energy. A typical photovoltaic cell includes a layer of a photoactive material and a layer of a charge carrier material disposed between a cathode and an anode. When incident light excites the photoactive material, electrons are released. The released electrons are captured in the form of electrical energy within the electric circuit created between the cathode and the anode.
In one type of photovoltaic cell, commonly called a dye-sensitized solar cell (DSSC), the photoactive material typically includes a semiconductor material, such as titania, and a photosensitizing agent, such as, for example, a dye. In general, the dye is capable of absorbing photons within a wavelength range of operation (e.g., within the solar spectrum).
In another type of photovoltaic cell, commonly referred to as a polymer thin film cell, the photoactive material used generally has two components, an electron acceptor and an electron donor. The electron acceptor can be a p-type polymeric conductor material, such as, for example poly(phenylene vinylene) or poly(3-hexylthiophene). The electron donor can be a nanoparticulate material, such as for example, a derivative of fullerene (e.g., 1-(3-methoxy carbonyl)-propyl-1-1-phenyl-(6,6) C61, known as PCBM).
Photovoltaic cells can be electrically connected together in series and/or in parallel to create a photovoltaic module. Typically, two photovoltaic cells are connected in parallel by electrically connecting the cathode of one cell with the cathode of the other cell, and the anode of one cell with the anode of the other cell. In general, two photovoltaic cells are connected in series by electrically connecting the anode of one cell with the cathode of the other cell.